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View Full Version here: : 31mm T5 Vs 30mm XW


chunkylad
28-02-2007, 03:55 PM
Hi All

I am considering adding a premium widefield ep to my collection. I'm tossing up between the 27mm Pano, the 30mm XW Pentax and 31mm T5 Nagler. I'm leaning towards either the Nagler or the XW. I'm not sure the extra width in the FOV of the Nagler is worth an extra $300 odd though.:shrug:

The ep is for my 305mm Newtonian @ f5.

Your thoughts would be appreciated.

Cheers

janoskiss
28-02-2007, 04:19 PM
Geez I wish I had your problem. With that much cash at stake I'd be wanting to spend a fair bit of time with both EPs in my scope on a good night before buying - preferably with the Virgo cluster riding high.

astropolak
28-02-2007, 06:02 PM
Very interesting...
Perhaps someone would be willing to compare the eyepieces side by side and document their findings for us. I can make my WO 28mm UWAN available to throw into the mix..

Joe

chunkylad
28-02-2007, 10:13 PM
Yeah Steve. I'm hoping to scrounge some time with at least one of these EPs at our next TAC observing night. Not an easy task considering I never get there before 11pm (work committments), so it's only the stayers left by the time I arrive:juggle: .

Cheers

Starkler
28-02-2007, 10:17 PM
Ive got 31 and 26mm naglers, I just wish I could :whistle: borrow :whistle: a 30mm XW for a thorough comparison .

Ambermile
01-03-2007, 01:10 AM
I tried the 31mm Nagler against the 35mm Pan last weekend - have to say that the FOV was similar between the two, the 31 was more contrasty too. Somehow though, the pan was oddly more comfortable over the long haul... There's just too much to see in the 31mm with that spacewalk thing - it's like with the pan it's all there without having to look around for stuff!

Not tried the Pentax I'm afraid but is the 31mm worth the difference between it and the 35mm pan? I'd say yes, definitely, if only for the improved contrast (this may be because of the higher mag but I think not)

So, my point? If you want the extra FOV that you would get from the 31mm and if you spend lots of eyetime at the scope then go for the 35mm Pan - your eyes will thank you for it.

Arthur

Zubenel
01-03-2007, 06:46 AM
Hi ,
For a fraction if the cost try a 55mm Televue plossl. It has a wider fov than any of them. Cant say I have tried it as i am not allowed it till tomorrow( my birthday):thumbsup: but the text books say it shouldn't work in my scope but Astroron's 55mm uo ep is just stunning.
Zub

Ambermile
01-03-2007, 07:15 AM
True, it's cheaper and the FOV is nice but it doesn't cut it on the edge and loses out on contrast as well. Moving from the 55mm to the 35mm Pan you really do notice that the "closed in" feeling you just had has gone. I think the expensive TV EP's really do spoil you once you use them but I also think they are worth it.

Mind you, the 55m is big and wide and is a great EP in it's own right. It's just not a Panoptic or a Nagler:shrug:

Arthur

skies2clear
01-03-2007, 07:21 AM
Trouble is, Chunkylad needs it for his 12" F5, so a 55mm eyepiece is giving too large an exit pupil, 11mm to be precise, which is a total waste of light. Even a 35 mm eyepiece, with 7mm exit pupil at F5, is pushing it IMO. So these long FL eyepieces are not that great for fast newtonians.

I haven't directly compared the 31T5 with the 30XW, but did seriously consider buying the 31T5, even though they cost a fortune here. A few other experienced observers talked me out of it in the end. I ended up getting a 30XW for a good price, and am totally happy with it, performance wise and total ease/comfort of use.

Tough choice though!

Clear skies

skies2clear
01-03-2007, 07:35 AM
I'd just like to add another opinion, though I can't back it up with proof. When comparing the apparent field of view of the XW at 70 deg, with a couple of other 80 deg plus eyepieces I have , including a Nagler (not the 31T5), the Pentax doesn't seem in practice to look much "smaller". I've compared the XW to other 69 or 70 deg eyepieces and it appears wider than those for some reason. When I compare the XW to these and hold them side by side to my 2 eyes looking through, the XW is actually wider, and by more than 1 or 2 degrees. Either Pentax are very conservative with their specifications, or the other eyepieces I have don't meet their specs. Or I'm imagining it, but I don't think so.

If I was to put a figure to it, the XW seems to be more like 75 deg compared with some other 68 to 70 deg eyepieces (including the TMB 40mm Paragon). There's no doubt to me many of the cheaper widefields aren't quite as widefield as they claim.

In any case, I think if I was shelling out nearly a grand for an eyepiece, I'd want to look through one first, if possible.

Clear skies

janoskiss
01-03-2007, 10:15 AM
Arthur, IMO the Panos are not in the same league optically as the 30mm XW, the latter being practically aberration free right across the FOV at f/5 and superior comfort. Like S2S says 55mm Plossl is not a good choice for an f/5 scope.

S2S, Pentax EPs I've used, XWs and XFs, seem to be spot on wrt specs. 70 and 60 degree FOV, 20 and 18mm eye relief, resp. No more no less.

skies2clear
01-03-2007, 12:32 PM
Thanks Steve, you are probably right about the Pentax specs. I must be comparing to other widefields that don't meet their published specs. eg.When doing a side by side comparison with even another decent quality wide field like the TMB (69 deg), the Pentax was easily 5 deg or more wider, not 1 degree as it should have been! You should hardly notice 1 degree difference I would think.

I wasn't saying the XW's are as wide as Naglers. They are not, but in terms of easily usable field, and this is very personal no doubt, they don't really lose much at all. Anyone agree or disagree with this? :shrug:

In the end, both of these (31T5 and 30XW) are premium chunks of glass and do perform extremely well,

Very Clear skies !

chunkylad
01-03-2007, 03:59 PM
Hi guys.

Thanks for the discussion. The question of side by side comparison still remains. I'm hoping someone can shed some light on the subject (no pun intended:D ) until I can get an opportunity to make a direct comparison myself.
Cheers

Ambermile
01-03-2007, 06:30 PM
Yoo may be right about the Pentax, I can only comment on the EP's I have, but to me the 35 pan was more comfortable for extended viewing. That "huge" FOV gets a bit straining after a while ;)

As for the 55mm, technically an f/5 newt would have issues yes - I have noticed only small a drop in contrast in mine (f/4.8) with it. Sometimes the figures don't add up at the scope I guess?

Arthur

Zubenel
18-03-2007, 08:29 PM
I remember reading an article in which Al Nagler said that as far a too large an exit pupil for a given scope was concerned , what did it matter if you wasted light , as long as the "experience was rewarding". Here is a quote taken from Cloudy nights.
""Exit Pupil Upper Limit: commonly quoted as 7mm, any larger exit pupil "wasting light." This is totally incorrect. For a refractor, there is no upper limit to exit pupil. With an obstructed system, the exit pupil limit is reached only when the secondary shadow becomes obtrusive in the image. You can work out the math yourself - a given telescope operating at an exit pupil of 10mm will give the brightest possible view of any object at that magnification.
It is only "wasted light" if you bought the telescope knowing you would always use it at 10mm exit pupil.""
However , the 31mm t5 and 35mm pan will give a more contrasty view because of the higher magnification.
Sorry for getting off topic
I think my next ep will be a 35 pan anyhow!!:)